A method for calculating a prediction motion vector of a block to be coded, by performing a median operation using motion vectors of neighboring blocks. If one of the neighboring blocks has motion vectors MV1 and MV2, direction (forward or backward) information of reference pictures referred to, respectively, by the motion vectors are acquired and one of the motion vectors is selected with reference to the acquired direction information. Then, the median operation including the selected motion vector is performed to obtain the prediction motion vector of the block to be coded.